The exaptation of manual dexterity for articulate speech: an electromyogram investigation

Electromyogram recordings revealed a concurrent contraction of the orbicularis oris, the primary articulator for bilabial stops, when participants executed a precision grip contracting the abductor pollicis brevis, a point motor act contracting the extensor indicis proprius or a curl motor act contracting the flexor sublimis digitorum (FDS). In contrast, the concurrent contraction of several facial muscles not directly involved in labial articulation was not observed during these acts. The results converge both with observations of sympathetic hand and mouth activity among nonhuman primates and prelinguistic human infants and with demonstrations of the influence of grasping on labial articulation in adult humans (e.g., Gentilucci et al., J Neurophysiol 86, 1685-1699, 2001). The findings are also consistent with theories suggesting the transition from gestural to verbal, articulate communication systems may be subserved by the properties of the human equivalent of monkey F5 mirror and canonical neurons located in Broca's area.